1. Field of the Invention
The present invention relates to semiconductor memory devices and to driving a plurality of wordlines during burn-in of a device with a row decoder having limited driving ability.
2. Description of the Related Art
Advances in semiconductor technology have increased the capabilities of semiconductor devices and made the devices smaller. In particular, the demand for semiconductor memory devices having large capacity has rapidly increased with the development of computers. In response to that demand, semiconductor memory devices have become smaller while still providing large storage capacity. Accordingly, memory cells in the semiconductor memory devices must be small, and the row decoders for selecting the memory cells are correspondingly small. Such row decoders commonly include NMOS transistors for decoding received row addresses. These NMOS transistors must be small to make the row decoders compact. Accordingly, the driving abilities of the row decoders are small.
To improve the reliability of the semiconductor memory devices, a wafer containing a plurality of semiconductor memory devices often undergoes a burn-in test process. The wafer burn-in test process applies burn-in stress to the wafer and functionally tests the semiconductor memory devices on the wafer. In particular, the burn-in test sequentially or simultaneously activates wordlines in the semiconductor memory devices while applying the burn-in stress to the wafer. Simultaneously activating multiple wordlines during the burn-in test may require a driving ability that is greater than the driving ability of the row decoder, particularly when the row decoder is small. As a result, the row decoder used for normal memory accesses cannot drive a plurality of wordlines during the wafer burn-in, which results in an incomplete wafer burn-in test. Accordingly, the semiconductor memory devices that pass the burn-in test may be unreliable.